The requirement for a mechanism to retain a gate in either the closed or open position is an old one for which there are many solutions. Many retainers rely on the concerted action of A number of moving parts and the interdigitation of various elements with varying degrees of precision. Such systems are necessarily vulnerable to corrosion and fouling. These difficulties are most pronounced where the gate is bulky, the forces exerted on the gate are great, or the gate is found in an environment in which wear will be considerable. In these circumstances, a simple retainer which emphasizes reliability over elegance is usually preferable.
One of the most demanding applications for retainers is on the discharge chutes of railway hopper cars. An exemplary chute is described in U.S. Pat. No. 5,046,432 to Bowler (1991). In a typical arrangement, a frame is fastened to the underside of the hopper car. The frame encloses a gate which is permitted to slide longitudinally in the frame between the open and closed position. The weight of the material within the hopper car tends to press against the gate with great force. For that reason, the gate is ordinarily formed from steel. The gate is, therefore, usually quite heavy and also prone to corrosion. The gate retainer in the Bowler patent, a flat bar of spring steel, pressed against the back upper edge of the gate slide and tended to damage the finish on the top of the slide, promoting corrosion.
A variety of locking or retainer mechanisms have been emloyed on bulk material handling container gates. A pawl and plunger latching mechanism may be used to hold a shaft against rotation, as in U.S. Pat. No. 3,138,117 to Dorey (1964). An upright latch plate with a pivot mount may be arranged so that a finger enters a notch to lock the gate against sliding, as in U.S. Pat. No. 3,780,672 to Fuller (1971) and U.S. Pat. No. 3,865,046 to Fuller (1975). In a similar arrangement, locking tabs may be placed so as to engage corresponding notches in the slide gate, as in U.S. Pat. No. 4,785,966 to Waltke (1988). Or, a locking dog can be positioned to rotate into place behind the sliding gate, as in U.S. Pat. No. 3,255,714 to Dorey (1966). These retaining mechanisms all depend on moving parts and the interdigitation of various elements. As a result, corrosion and fouling with dirt or other material may interfere with their effectiveness. In addition, these retainers typically require an operator to actively engage their various mechanisms. This can be awkward and indeed dangerous to the operator.